Polyomaviruses are ubiquitous silent pathogens in a variety of vertebrate hosts, including humans, but become opportunistic pathogens in the setting of depressed immune function. By early adolescence, nearly all humans are infected by both of the two known polyomaviruses, BKV and JCV. Reactivation of BKV is a leading cause of kidney transplant rejection and, in the elderly and AIDS patients, JCV reactivation causes the progressive fatal central nervous system (CNS) demyelinating disease called Progressive Multifocal Leukoencephalopathy (PML). PML also occurs in conjunction with immunosuppressant drug regimens. Recently, several patients treated with Tysabri, a humanized VLA-4 antibody that controls relapses in multiple sclerosis patients by restricting T cell immigration to the CNS, developed PML. There is currently no clinically effective antiviral therapy for polyomavirus infection, or the consequences of reactivation. Repetitive antigen encounter during persistent infection causes functional debilitation of virus-specific T cells, with clonal deletion the eventual consequence of chronic TCR engagement. The duration and magnitude of persistent viral infection govern the survival of memory T cells and their ability to limit viral replication. Thus, therapeutics that lower viral load will promote generation of effective antiviral T cell memory. Because of the narrow host range of this virus family, the mouse-polyoma virus (PyV) system provides the only tractable model to evaluate pathogenesis of and immunity to this clinically important virus family, and to develop and test novel therapeutic compounds. We recently found that Abl-family tyrosine kinases are required for replication of PyV and that inhibitors of these kinases (e.g. Novartis' Gleevec), rationally designed to control specific human cancers (e.g., Philadelphia chromosome+ chronic myelogenous leukemia), block PyV replication both in vitro and in mice. In this exploratory application application, we have combined the expertise of the Drs. Aron Lukacher (mouse polyoma virus pathogenesis and viral immunology) and Daniel Kalman (tyrosine kinases, Abl-family inhibitory compounds, virion-host cell interaction, deconvolution fluorescence microscopy) to investigate mechanism(s) of inhibition by these compounds in vitro and their capacity to limit PyV infection in vivo. In Specific Aim 1, we will test the hypothesis that Abl-family tyrosine kinases are involved in early steps in PyV cell uptake and intracellular trafficking and in replication. Because of the importance of CD8 T cells in immunosurveillance for polyomavirus-infected cells, and the detrimental effect of persistent viral infections on memory T cell survival and function, we further hypothesize that reductions in viral load mediated by the Abl-family kinase inhibitors will improve memory polyomavirus-specific CD8 T cell responses and further curtail polyomavirus reactivation (Specific Aim 2). Investigation of the mechanism of inhibition by these compounds and their capacity to limit PyV infection in vivo will provide proof-of-principle for their therapeutic use to counter polyomavirus reactivation in high-risk populations. Project Narrative: Nearly all individuals are infected lifelong by two human polyomaviruses, otherwise silent infections that have debilitating, potentially fatal, consequences in immunosuppressed individuals (e.g., kidney transplant recipients, HIV/AIDS). There is no effective antiviral therapy for polyomavirus infection. In this application, studies are proposed to explore the mechanism for the novel observation that compounds that inhibit Abl- family tyrosine kinases (e.g., FDA-approved Gleevec) limit polyomavirus infection, a critical prelude for their potential therapeutic use to prevent polyomavirus reactivation in immunosuppressed individuals. [unreadable] [unreadable] [unreadable]